Communications Cable with Improved Isolation Between Wire-Pairs and Metal Foil Tape

ABSTRACT

A communications cable having a plurality of twisted pairs of conductors and various embodiments of a metal foil tapes between the twisted pairs and a cable jacket is disclosed. In some embodiments, a metal foil tape includes a discontinuous metal layer and a polymer layer bonded to the metal layer. Portions of the metal layer and the polymer layer are deformed to form a plurality of dimples, the dimples forming air gaps between the polymer layer and the cable core or a barrier layer if used. The air gaps lower the overall dielectric constant between the metal layer and the cable core, thereby lowering the alien capacitance of the communications cable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/543,064, filed Aug. 9, 2017, the subject matter of which is herebyincorporated by reference in its entirety.

BACKGROUND

As networks become more complex and have a need for higher bandwidthcabling, attenuation of cable-to-cable crosstalk (or “alien crosstalk”)becomes increasingly important to provide a robust and reliablecommunications system. Alien crosstalk is primarily coupledelectromagnetic noise that can occur in a disturbed cable arising fromsignal-carrying cables that run near the disturbed cable, and, istypically characterized as alien near end crosstalk (ANEXT), or alienfar end crosstalk (AFEXT). To attenuate alien crosstalk, continuous ordiscontinuous metal foil tape may be wrapped around the inner core of acommunications cable. Unterminated continuous metal foil tape cablesystems can have unwanted electro-magnetic radiation and orsusceptibility issues. A discontinuous metal foil tape cable systemgreatly reduces the electro-magnetic radiation and or susceptibilityissues.

SUMMARY

A communications cable having a plurality of twisted pairs of conductorsand various embodiments of a metal foil tapes between the twisted pairsand a cable jacket is disclosed. In some embodiments, a metal foil tapeincludes a discontinuous metal layer and a polymer layer bonded to themetal layer. Portions of the metal layer and the polymer layer aredeformed to form a plurality of dimples, the dimples forming air gapsbetween the polymer layer and the cable core or a barrier layer if used.The air gaps lower the overall dielectric constant between the metallayer and the cable core, thereby lowering the alien capacitance of thecommunications cable.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description references the drawings, wherein:

FIG. 1 is an illustration of a perspective view of a communicationssystem;

FIG. 2 is an illustration of a transverse cross-sectional view of acommunications cable;

FIG. 3 is an illustration of a lengthwise cross-sectional view of ametal foil tape and barrier tape; and

FIG. 4 is an illustration of a bottom view of a metal foil tape.

DETAILED DESCRIPTION

Reducing the diameter of cabling systems, such as Category 6A cablingsystems, is desirable because it allows for increased cabling density asnetworks become more complex. However, reducing cable diameter can bringthe metal foil tape included therein closer to the conductor pairs ofthe cable, which can raise the internal capacitance between wire pairsand between wires within a pair of the cable. If the metal foil tape isphysically close to the twisted wire pairs, a capacitive coupling canoccur. This capacitive coupling can create effect the wire pair'simpedance (reducing the return loss) and create coupling between wirepairs (i.e., both near and far end crosstalk).

Examples disclosed herein illustrate communications cable designs thatinclude various embodiments of metal foil tapes (i.e., discontinuousmetal foil tapes) positioned between the jacket and unshielded conductorpairs of the cables. The disclosed metal foil tapes may include dimplesprotruding inward toward the core of the cable which create space (i.e.,air gaps) between the metal layer of the metal foil tapes and the cablecore (or barrier tape, if used). The air gaps decrease the overalleffective dielectric constant between the metal foil and the cable core,thereby reducing the internal capacitance of the communications cable.

Reference will now be made to the accompanying drawings. Whereverpossible, the same reference numbers are used in the drawings and thefollowing description to refer to the same or similar parts. It is to beexpressly understood, however, that the drawings are for illustrationand description purposes only. While several examples are described inthis document, modifications, adaptations, and other implementations arepossible. Accordingly, the following detailed description does not limitthe disclosed examples. Instead, the proper scope of the disclosedexamples may be defined by the appended claims.

FIG. 1 is a perspective view of a communications system 20, whichincludes at least one communications cable 22, connected to equipment24. Equipment 24 is illustrated as a patch panel in FIG. 1, but theequipment can be passive equipment or active equipment. Examples ofpassive equipment can be, but are not limited to, modular patch panels,punch-down patch panels, coupler patch panels, wall jacks, etc. Examplesof active equipment can be, but are not limited to, Ethernet switches,routers, servers, physical layer management systems, andpower-over-Ethernet equipment as can be found in datacenters/telecommunications rooms; security devices (cameras and othersensors, etc.) and door access equipment; and telephones, computers, faxmachines, printers and other peripherals as can be found in workstationareas. Communications system 20 can further include cabinets, racks,cable management and overhead routing systems, and other such equipment.

Communications cable 22 is shown in the form of an unshielded twistedpair (UTP) cable, and more particularly a Category 6A cable which canoperate at 10 Gb/s, as is shown more particularly in FIG. 2.Communications cable 22 may, however, be a variety of other types ofcommunications cables, as well as other types of cables. Communicationscable 22 can be terminated directly into equipment 24, or alternatively,can be terminated in a variety of plugs 25 or jack modules 27 such as anRJ45 type, jack module cassettes, and many other connector types, orcombinations thereof. Further, cables 22 can be processed into looms, orbundles, of cables, and additionally can be processed intopre-terminated looms.

Communication cable 22 can be used in a variety of structured cablingapplications including patch cords, backbone cabling, and horizontalcabling, although the present invention is not limited to suchapplications. In general, the present invention can be used in military,industrial, telecommunications, computer, data communications, and othercabling applications.

Referring to FIG. 2, there is shown a transverse cross-section ofcommunications cable 22, taken along section line 2-2 in FIG. 1.Communications cable 22 may include an inner cable core 23 with fourtwisted conductive wire pairs 26 that are separated with a pairseparator 28. Pair separator 28 may be formed with a clockwise rotation(left hand lay) with a cable stranding or lay length. An example laylength may be 3.2 inches. Pair separator 28 can be made of a plastic,such as a solid fire-retardant polyethylene (FRPE), for example.

A wrapping of barrier tape 32 may surround inner core 23. Barrier tape32 can be helically wound or longitudinally wrapped around inner core23. As shown in FIG. 2, the twisted pair conductors may extend beyondpair separator 28 to create an outer diameter of inner core 23. Theouter diameter may be, for example, approximately 0.2164 inches, and thecircumference may be 0.679 inches. In some implementations, barrier tape32 may wrap around inner core 23 slightly more than twice, and there maybe two applications of barrier tape 32 in some implementations. Barriertape 32 may be formed of a polymer or polymer-based material withnon-conductive additives. Barrier tape 32 may be a solid, foamed,embossed, or perforated construction. To minimize alien capacitance incommunications cable 22, barrier tape 32 may be designed such that ithas a relatively low dielectric constant, such as a dielectric constantthat approaches that of air (i.e., ε_(r)=1).

Metal foil tape 34 may be longitudinally wrapped around barrier tape 32under cable jacket 33 along the length of communications cable 22. Thatis, metal foil tape 34 may be wrapped along its length such that itwraps around the length of communications cable 22 in a “cigarette”style wrapping. Alternatively, metal foil tape 34 may be helicallywrapped around barrier tape 32.

As shown in FIG. 3, metal foil tape 34 may comprise a metal (e.g.,aluminum) layer 35 adhered to a polymer film support layer 36. In someimplementations, metal layer 35 may be adhered to polymer layer 36 withan adhesive such as a glue. Metal foil tape 34 may be wrapped aroundbarrier tape 32 such that metal layer 35 faces jacket 32 and polymerlayer 36 faces inward toward inner core 23. An additional polymer layer(i.e., slick layer 38) may be applied to the top of metal layer 35(e.g., at a 1 mil thickness) to assist in the manufacturing processwithout affecting the electrical performance of communications cable 22.

Discontinuities 37 may be created in metal layer 35, for example, in apost-processing step where lasers are used to ablate portions of metallayer 35. Discontinuities 37 may run in the longitudinal direction ofcommunications cable 22 (i.e., along the length of communications cable22), in the latitudinal direction of communications cable 22 (i.e.,orthogonal to the length of communications cable 22), or combinationsthereof. For example, discontinuities 37 may run both in thelongitudinal and latitudinal directions of communications cable 22 toform a “brick” pattern in metal layer 35 when viewed from the top down.

The thickness of layers 35, 36, and 32, as well as the dielectricconstants of the non-metal layers, may determine the capacitance ofcommunications cable 22. Since it is desired to reduce the overall sizeof communications cable 22, in order to lower the capacitance ofcommunications cable 22, the present disclosure describes a metal foiltape 34 that lowers the effective dielectric constant of communicationscable 22, which in turn lowers the alien capacitance of communicationscable 22.

To lower the effective dielectric constant of communications cable 22,the disclosed metal foil tape 34 is formed to include dimples 39 thatprotrude toward inner core 23. Dimples 39 may be U-shaped depressionsformed in the metal layer 35 and polymer layer 36. Dimples 39 may becircular in shape or other shapes (e.g., elliptical, oblong, oval,etc.). Dimples 39 create air gaps (i.e., space filled with air) betweenbarrier tape 32 and flat portions 40 of polymer layer 36. The air in theair gaps have a much lower dielectric constant than the polymer materialof polymer layer 36, thereby reducing the effective dielectric constantof communications cable 22. By adjusting the height of dimples 39 andthe spacing between neighboring dimples 39, the effective relativedielectric constant between inner core 23 and metal layer 35 can bereduced.

As an example, in FIG. 3, dimples 39 may be a height of 2 mils, flatportions 40 of polymer layer 36 may be a height of 1 mil, metal layer 35may be a height of 0.3 mil, slick coating 38 may be a height of 1 mil,and barrier layer 32 may be a height of 6.7 mils. The total thickness inthis example between inner core 23 and cable jacket 33 is 11 mils, andthe total thickness between inner core 23 and metal layer 35 is 9.7mils. With dimples 39 in metal foil tape 34, the overall effectivedielectric constant between inner core 23 and metal layer 35 is ε=1.39.Accordingly, the corresponding capacitance may be calculated to be 7.4pF/cm², which is a significant reduction in capacitance compared to asimilar cable having no dimples (which may have a capacitance of 11pF/cm²). The significant reduction in capacitance allows for eventhinner barrier tapes to be used, thereby reducing the overall thicknessof communications cable 22 even further.

Dimples 39 may be formed in various patterns. For example, as shown inFIG. 4, dimples 39 may be formed in staggered rows. The staggering mayrun along the longitude of communications cable 22 or transverse tocommunications cable 22. The layout of dimples 39 may be optimized forbest mechanical strength while keeping potential processing limitations(e.g., material or process related) in mind.

For example, the pattern of dimples 39 may be optimized to accommodate adisadvantage to dimpling after the laser processing has createddiscontinuities 37 through abatement of material in metal layer 35. Theabatement process may produce a metal slit-width (or kerf) approximately0.002 to 0.004 inches wide in metal layer 35. Metal foil tape 34 may berun through dimpling tooling to form dimples 39 after the abatementprocess has been completed. The dimpling tooling may include a rollingdie set having a having a first hardened roller with protrusions and asecond roller either elastic in nature or hardened with matchingdepressions sequenced to the first hardened roller. The protrusionsdeform portions of metal layer 34 and polymer layer 36 outwards suchthat the portions are displaced in a U-shape. The dimpling tooling maycause a change in the geometry of the kerf such that the kerf isdisturbed if a dimple 39 is formed on or near the kerf. The disturbancemay cause metal from metal layer 35 to stretch in such a manner that theelectrical discontinuities 37 created via the abatement process aredestroyed. Accordingly, dimples 39 may be patterned such that theyenlarge the kerf verses collapse the kerf, or such that dimples 39 areplaced were metal abatement will not occur.

The actual processing steps of dimple formation may be optimized toachieve desired embossing features on metal foil tape 34. For example,dimples 39 processing steps may be optimized by either actively avoidingthe formation of dimples 39 near the kerf or by forming dimples 39 priorto the metal abatement process such that the kerf is formed afterdimples 39. Moreover, the dimpling process can be employed in varioussteps of cable manufacturing to optimize its application tocommunications cable 22. For example, separate from the cablemanufacturing process, the dimpling tooling may be utilized in adimpling station on the laser abatement machine, pre or post laserabatement, and prior to metal foil tape rewind. As another example, thedimpling station can be utilized on a stand-alone web handling machinewith. As a further example, the dimpling station can be utilized at apoint-of-use of the metal foil tape during cable manufacture, such as atcable jacket application or cable stranding. Staging the dimplingstation at point-of-use of the metal foil tape allows for thepre-dimpled tape to occupy much less space when wound on a bobbin,thereby saving on space during transport of the tape from lasering tocabling/jacketing. Moreover, once the tape is dimpled, the dimples areexposed to the possibility of being damaged (i.e., flattened).Accordingly, by waiting to dimple the metal foil tape just before it isapplied to the cable reduces the risk of damage to the dimples.

Note that while the present disclosure includes several embodiments,these embodiments are non-limiting (regardless of whether they have beenlabeled as exemplary or not), and there are alterations, permutations,and equivalents, which fall within the scope of this invention.Additionally, the described embodiments should not be interpreted asmutually exclusive, and, should instead be understood as potentiallycombinable if such combinations are permissive. It should also be notedthat there are many alternative ways of implementing the embodiments ofthe present disclosure. It is therefore intended that claims that mayfollow be interpreted as including all such alterations, permutations,and equivalents as fall within the true spirit and scope of the presentdisclosure.

1. A communications cable, comprising: a jacket; a cable core comprisinga plurality of twisted pairs of conductors; a metal foil tape disposedbetween the cable core and the jacket, the metal foil tape comprising: adiscontinuous metal layer; a polymer layer bonded to the metal layer;and a plurality of solid dimples formed by deforming portions of themetal foil tape, the solid dimples forming air gaps between the polymerlayer and the cable core, the air gaps lowering an overall dielectricconstant between the metal layer and the cable core.
 2. Thecommunications cable of claim 1, wherein the dimples are formed in apattern along the longitude of the communications cable.
 3. Thecommunications cable of claim 1, wherein the dimples are formed in apattern along the latitude of the communications cable.
 4. Thecommunications cable of claim 3, wherein the pattern is a pattern ofstaggered rows.
 5. The communications cable of claim 1, wherein themetal layer faces the jacket.
 6. The communications cable of claim 5,wherein the polymer layer faces the cable core.
 7. The communicationscable of claim 1, wherein the dimples protrude toward the cable core ofthe communications cable.
 8. A communications cable, comprising: ajacket; a cable core comprising a plurality of twisted pairs ofconductors; a barrier layer between the cable core and the jacket; and ametal foil tape disposed between the barrier layer and the jacket, themetal foil tape comprising: a discontinuous metal layer; a polymer layerbonded to the metal layer; and a plurality of U-shaped dimples formedthereon, the dimples forming air gaps between the polymer layer and thebarrier layer, thereby lowering an overall dielectric constant betweenthe metal layer and the cable core.
 9. The communications cable of claim8, wherein the dimples are circular shaped.
 10. The communications cableof claim 8, wherein the dimples are elliptical or oval shaped.
 11. Amethod for manufacturing a communications cable, comprising: forming acable core comprising a plurality of twisted pairs of conductors; andforming a barrier layer on the cable core; at a point-of-applicationstep of applying a metal foil tape on the barrier layer, creatingdimples by deforming a metal layer and a polymer layer of the metal foiltape; and after the dimples have been created, applying the metal foiltape onto the barrier layer.
 12. The method of claim 11, wherein thepoint-of-application step is a cable jacket application step.
 13. Themethod of claim 12, wherein creating the dimples in the the metal foiltape at the cable jacket application step includes creating the dimplesat a dimpling station between tape payoff of the metal foil tape priorto a jacket extrusion die.
 14. The method of claim 11, wherein thepoint-of-application step is a cable stranding step.
 15. The method ofclaim 14, wherein creating the dimples in the the metal foil tape at thecable stranding step includes creating the dimples at a dimpling stationbetween tape payoff of the metal foil tape prior to an application ofthe metal foil tape onto the barrier layer at a stranding machine.